Contoured Stator Shroud

ABSTRACT

A contoured stator shroud has a stator chord overhang having a surface which varies in elevation forming a plurality of surface contours, wherein the contours reduce clearance between adjacent vanes during off design performance positioning of the vanes.

CROSS-REFERENCE TO RELATED APPLICATIONS

None

BACKGROUND

The disclosed embodiments generally pertain to gas turbine engines. More particularly, present embodiments relate to shrouds within gas turbine engines which are utilized with pivoting vanes.

In a gas turbine engine a typical gas turbine engine generally possesses a forward end and an aft end with its several components following inline therebetween. An air inlet or intake is at a forward end of the engine. Moving toward the aft end, in order, the intake is followed by a compressor, a combustion chamber, a turbine, and a nozzle at the aft end of the engine. It will be readily apparent from those skilled in the art that additional components may also be included in the engine, such as, for example, low-pressure and high-pressure compressors, high-pressure and low-pressure turbines, and an external shaft. This, however, is not an exhaustive list. An engine also typically has an internal shaft axially disposed through a center longitudinal axis of the engine. The internal shaft is connected to both the turbine and the air compressor, such that the turbine provides a rotational input to the air compressor to drive the compressor blades.

In operation, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream through turbine stages. These turbine stages extract energy from the combustion gases. A high pressure turbine first receives the hot combustion gases from the combustor and includes a stator nozzle assembly directing the combustion gases downstream through a row of high pressure turbine rotor blades extending radially outwardly from a supporting rotor disk. In a two stage turbine, a second stage stator nozzle assembly is positioned downstream of the first stage blades followed in turn by a row of second stage rotor blades extending radially outwardly from a second supporting rotor disk. The turbine converts the combustion gas energy to mechanical energy.

Vanes or airfoils are typically designed with a primary or optimal position for operation. However, depending on the desired operating condition of the turbine engine, the vanes may be actuated to alternate positions. Current stator shroud designs utilize a circular cross-section across which vanes are actuated. As the vanes move from the open design position to off design closed positions, clearance between the vane and shroud increases due to the curvature of the shroud, the flow path geometry and the lower edge shape of the vane, all of which are required to meet the compressor operating requirements.

When this clearance increases, flow disruptions can affect the intended purpose of the vane shape function and configuration. It would be desirable to overcome these and other deficiencies so that the clearance between the vane and shroud is reduced, for example in the off design closed angular positions of the vane.

SUMMARY

According to at least some embodiments, a contoured stator shroud vane assembly in a gas turbine engine having an inlet end, an outlet end and a plurality of propulsor components comprises a stator shroud having a generally circular cross-section, the shroud having a forward end, an aft end and at least one surface extending between said first end and said second end, the shroud having a plurality of pivots disposed circumferentially about the shroud to support a trunnion of a vane, the at least one surface of varying elevation adjacent to said plurality of pivots and extending in a circumferential direction.

According to at least some embodiments, a contoured stator shroud, comprises a forward end, an aft end and at least one surface extending between the forward end and the aft end, the at least one surface being tapered from the forward end to the aft end, a plurality of areas of varying elevation disposed about the at least one surface, the plurality of areas each having a peak and a valley, a plurality of pivot apertures spaced about a forward end of the at least one surface.

According to still other embodiments, a contoured stator shroud, comprises a forward end and an aft end, at least one surface extending between the forward end and the second end, the at least one surface having a scalloped chord overhang area, the scalloped area extending in a circumferential direction, a plurality of vane mounting locations disposed circumferentially between the forward end and the aft end.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments of the invention are illustrated in the following illustrations.

FIG. 1 is a side section view of a gas turbine engine;

FIG. 2 is an exploded perspective view of a stator shroud vane assembly;

FIG. 3 is a perspective view of the stator shroud vane assembly;

FIG. 4 is a side section view of an exemplary stator shroud vane assembly;

FIG. 5 is a detail perspective view of stator shroud vane assembly;

FIG. 6 is an aft view of the stator shroud vane assembly in a first position;

FIG. 7 is an aft view of the stator shroud vane assembly in a second position;

FIG. 8 is an aft view of the stator shroud vane assembly in a third position; and,

FIG. 9 is a graph of vane position as related to clearance between the shroud and the vane.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments provided, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not limitation of the disclosed embodiments. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present embodiments without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to still yield further embodiments. Thus it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

Referring to FIGS. 1-9, various embodiments of a contoured stator shroud capable of use with pivoting vanes. The stator shroud includes a stator shroud overhang surface over which vanes are pivoted during engine operation. The stator shroud overhang surface has varying elevations to eliminate leakage between the vane and the shroud which would normally occur when a vane pivots an outer surface of the shroud. This reduces any flow disruptions or flow disturbances along the vane or airfoil.

As used herein, the terms “axial” or “axially” refer to a dimension along a longitudinal axis of an engine. The term “forward” used in conjunction with “axial” or “axially” refers to moving in a direction toward the engine inlet, or a component being relatively closer to the engine inlet as compared to another component. The term “aft” used in conjunction with “axial” or “axially” refers to moving in a direction toward the engine nozzle, or a component being relatively closer to the engine nozzle as compared to another component.

As used herein, the terms “radial” or “radially” refer to a dimension extending between a center longitudinal axis of the engine and an outer engine circumference. The use of the terms “proximal” or “proximally,” either by themselves or in conjunction with the terms “radial” or “radially,” refers to moving in a direction toward the center longitudinal axis, or a component being relatively closer to the center longitudinal axis as compared to another component. The use of the terms “distal” or “distally,” either by themselves or in conjunction with the terms “radial” or “radially,” refers to moving in a direction toward the outer engine circumference, or a component being relatively closer to the outer engine circumference as compared to another component.

As used herein, the terms “lateral” or “laterally” refer to a dimension that is perpendicular to both the axial and radial dimensions.

Referring initially to FIG. 1, a schematic side section view of a gas turbine engine 10 is shown having an engine inlet end 12 wherein air enters the propulsor 13 which is defined generally by a compressor 14, a combustor 16 and a multi-stage high pressure turbine 20. Collectively, the propulsor 13 provides thrust or power during operation. The gas turbine 10 may be used for aviation, power generation, industrial, marine or the like. Depending on the usage, the engine inlet end 12 may alternatively contain multi-stage compressors rather than a fan. The gas turbine 10 is axis-symmetrical about engine axis 26 or shaft 24 so that various engine components rotate thereabout. In operation air enters through the air inlet end 12 of the engine 10 and moves through at least one stage of compression where the air pressure is increased and directed to the combustor 16. The compressed air is mixed with fuel and burned providing the hot combustion gas which exits the combustor 16 toward the high pressure turbine 20. At the high pressure turbine 20, energy is extracted from the hot combustion gas causing rotation of turbine blades which in turn cause rotation of the shaft 24. The shaft 24 passes toward the front of the engine to continue rotation of the one or more compressor stages 14, a turbofan 18 or inlet fan blades, depending on the turbine design.

The axis-symmetrical shaft 24 extends through the through the turbine engine 10, from the forward end 12 to an aft end. The shaft 24 is journaled along its length. The shaft 24 may be hollow to allow rotation of a low pressure turbine shaft 28 therein and independent of the shaft 24 rotation. Both shafts 24, 28 may rotate about the centerline axis 26 of the engine. During operation the shafts 24, 28 rotate along with other structures connected to the shafts such as the rotor assemblies of the turbine 20 and compressor 14 in order to create power or thrust depending on the area of use, for example power, industrial or aviation.

Referring still to FIG. 1, the inlet 12 includes a turbofan 18 which has a plurality of blades. The turbofan 18 is connected by the shaft 28 to the low pressure turbine 19 and creates thrust for the turbine engine 10. The low pressure air may be used to aid in cooling components of the engine as well.

Referring now to FIG. 2 an exploded perspective view of a stator shroud vane assembly 30 is depicted. A plurality of vanes 40 are spaced about the shroud 32, most of which are not shown. Three vanes 40 are shown exploded from the outer surface of the shroud. For clarity sake, however, it should be understood that a plurality of vanes 40 are disposed about the shroud 32. The shroud 32 of the exemplary embodiment is circular in cross section and frusto-conical in shape having a forward end 34, an aft end 36. Within the hollow central portion of the shroud the propulsor components 13 of the gas turbine engine 10 may pass through. The exemplary shroud 32 is located in the compressor 14 area of the engine. For example, a multi-stage compressor typically includes several rows of rotating blades mounted on a rotor and several rows of stator vanes 40 mounted between a stator casing and the shroud 32. The shroud is axisymmetric to the shaft 24 (FIG. 1) of engine 10.

Near the forward end 34 are a plurality of pivots 38, which are represented in the exemplary embodiment as a number of circular pockets wherein the vanes 40 are seated for rotation relative to the shroud 32. The shroud 32 also tapers from a smaller diameter near the forward end 34 to a larger diameter near the aft end 36. As will be better understood upon further reading of this disclosure, a clearance is created between a lower edge of the vanes 40 and the outer surface of the shroud 32 when the vanes 40 are seated within the pivots 38. In a normal shroud, the circular cross-section results in increased clearance between the vane and the shroud when the vane is rotated to off design positions. However, present embodiments provide for a wavy or variable surface height to reduce clearance in the off-design positions of the vane 40.

The vane 40 includes an outer spindle 44 and an inner spindle 45. The spindles 44, 45 may be formed as a vertical line or at an angle to the vertical. For example, the depicted spindles are at an angle of between 10 and 15 degrees from the vertical. At the inner spindle 45 is a button 42 which along with the spindle 45 is seated within the pivot 38. An upper button 56 also controls rotation within the casing of the engine, through which the outer spindle passes.

Referring now to FIG. 3, a perspective view of a stator shroud vane assembly 30 is depicted. As previously described, the instant shroud assembly 30 is located within the compressor 14 of the turbine engine. However the principles embodied in the contoured stator shroud 32 may be utilized in alternate locations of the engine wherein shrouds and vanes or air foils are utilized, such as the stator vanes of a turbine, for example. The stator shroud 32 depicted is at an inner diameter of the vanes 40. An engine casing (not shown) may be used to provide the outer diameter pivot location for the vanes 40. The stator vane shroud assembly 30 utilizes a shroud 32 having a forward end 34 and aft end 36. The shroud 32 is generally circular in cross section as partially shown in the view depicted. The diameter at the forward end 34 may be larger than the diameter at the aft end 36. The forward end includes a plurality of pivots 38 wherein vanes 40 may be positioned. The pivots 38 are recessed areas wherein the vane or air foils 40 are positioned for pivoting utilizing buttons or guides 42. At a radially outward position of the vane 40 is a spindle 44 which may be utilized to mount the second end of the vanes 40 to provide guided pivoting or rotation. The spindle 44 may pass through an aperture in an engine casing to stabilize the spindle and allow for pivoting motion. A lever arm (not shown) guides the rotation through the desired angular displacement providing the different positions for improved efficiency and performance of the engine at multiple operating conditions. The plurality of vanes 40 extend about the circumference of the shroud 32 near the forward end 34 of the shroud, although some are not shown for clarity.

Extending rearwardly from the pivots 38 is at least one shroud surface 46, for example a stator chord overhang surface 46. The stator chord overhang surface 46 tapers from a smaller diameter near the pivots 38 to a larger diameter near the aft end 36. This axial direction taper or change in elevation may be curved or may be linear.

In addition to this taper, the stator chord overhang surface 46 is contoured so that the elevation changes in the circumferential direction. As shown with the broken lines 48 extending in the circumferential direction, the curvature 48 of the broken lines depicts the contour of the stator chord overhang surface 46 which varies between a lower elevation and an upper elevation in a circumferential direction. Thus rather than having a circular surface, the broken line depicts the contour 48 along wavy or sinuous surface 46. According to one embodiment of the present disclosure, the stator chord overhang surface 46 has a wavy contour 48 to reduce clearance between the vane 40 and the shroud 32 during movement of the vane 40. According to alternate embodiments, the variation in elevation in the circumferential direction may be linear. In either embodiment, the surface 48 includes a plurality of peaks and valleys. The axis of the peaks or valleys are generally parallel to the axis of the engine 26 (FIG. 1) or at an angle to engine axis 26 as the shroud tapers from forward to aft end. As will be described further herein, the contour 48 significantly reduces the flow field disruptions created by the clearance between the vanes 40 and shroud 32. These clearances would normally adversely affect the intended purpose of the vane airfoil shape, function and configuration when the vane moves between open and closed angular positions.

The exemplary vane or air foil 40 includes a leading edge 50, and a trailing edge 52 and opposed surfaces extending between. The opposed surfaces define a suction side and a pressure side which will be understood by one skilled in the art. At a radially outward end of the vane 40 an outer enlarged portion or button 56. The spindle or trunion 44 may be connected to a lever arm or other feature to actuate the vane 40 to a desired position. The rotation of the vane 40 provides more than one optimal condition for the vane or air foil to provide improved efficiency and performance at differing operating conditions of the gas turbine engine 10.

Near a lower end of the vane 40, a fillet 54 connects the vane 40 to the button 42 at the radially inner end. The lower edge 58 of the vane 40, or vane overhang, is curved and during movement of the vane 40, the lower edge 58 moves away from the typical shroud surface (FIG. 6) which is purely circular in cross section and represented by line 70. This creates clearance between the lower vane edge 58 and the chord overhang surface 46 due to the divergent geometries of the two parts. The increased clearance which occurs with prior art to systems reduces performance, air flow turn and increases loss in this region which is undesirable and inhibits improvements in engine performance. The contour represented by the wavy or curved broken line 48 decreases clearance between the shroud 32 and the vane 40 improving the air turning performance and reducing loss in this region.

Referring now to FIG. 4, a side section view of the assembly 30 of FIG. 3 is depicted. The shroud 32 is shown sectioned vertically between the forward end 34 and the aft end 36 so as to depict the button 42 which is seated within the pivot 38. The vane 40 further includes a lower spindle or trunnion 45 which extends downwardly into the pivot so that the vane 42 is pivotally secured in the shroud 32 and, as previously described, the upper spindle 44 is pivotally retained through an engine casing. As also shown in the figure, the stator chord overhang 46 is curved in the axial direction between the forward end 34 and the aft end 36, and more specifically aft of the pivots 38. According to alternative embodiments, the surface 46 is tapered linearly in the axial direction between forward end 34 and the aft end 36.

Referring now to FIG. 5, a detailed perspective view of the shroud 32 and vanes 40 are depicted. The detailed view shows a pivot 38 in both an empty condition and a filled by a vane 40. A button 42 is seated within the generally circularly shaped pivot 38 and the vane 40 is connected to the button 42 by fillet 54. Between a lower edge 58 of the vane and the stator chord overhang 46 a clearance 60 is shown. The clearance is reduced relative to prior art stators due to the curvature in the axial direction, between the forward end 34 and the aft end 36. Similarly, the clearance is decreased through the arcuate movement of the vane 40 within the pivot 38 due to the contour 48 along the circumferential direction of the overhang surface 46.

In the view of FIG. 5, the contour 48 is more clearly shown due to the curvature of the broken line 48 which represents the contour of the stator shroud 32. A plurality of axially extending contour lines 49 also are shown on the stator chord overhang surface 46 which depict another curvature of the stator 32. In combination with the lower edge 58 of the vane 40 decrease clearance between the vane 40 and stator 32 which improves engine performance through multiple positions of the pivoting vane 40. Relative to operation of the engine 10, the vanes 40 are closed when the engine speed is at or very near zero. In this closed position, the vanes 40 are near the uppermost elevation of the contour surface 48. Alternatively, as engine speed increases and approaches a maximum, the vane 40 approaches the lowermost elevation of the contour surface 48.

Referring now to FIGS. 6-8, the shroud 32 is shown in an aft view looking forward with a vane 40 shown move in multiple positions. The contour of the stator chord overhang surface 46 is best described in reference to this view. The wavy or sinuous surface 48 is formed by a plurality of scallop-like humps which change between first and second elevations. Although the term sinuous is used, it should not be limited to mathematically exact sin curve. The term is instead used in a general sense to indicate a repeating change in elevation. A broken line 70 is shown in the view to represent a circular reference shape of a prior art shroud. The line 70 may also represent a base or first elevation of the stator chord overhang surface 46. Alternatively, the line 70 of the instant embodiment may be above or below the valley or lower elevation of the stator chord overhang surface since, as shown, the surface 46 also changes elevation in the axial direction. The contour 48 elevation changes are shown by referencing the difference between first elevation 70 and the second upper elevation 72 of the contour. Thus the overhang surface 46 changes elevation between a first elevation and a second elevation and with such changing elevation, the clearance between the vane 40 is reduced throughout the positions depicted in FIGS. 6-8.

The vane 40 may rotate from, for example, minus 3 degrees and about 25 degrees. Thus the exemplary vane 40 may move about 14 degrees from the center position in either of two rotational directions. However this is exemplary and alternate angular ranges may be designed into the vane movement.

Referring now to FIG. 7, the vane is shown in a central position which more clearly depicts the lower edge 58 of the vane. The vane 40 is in the 11 degree position, according to the exemplary range as previously described. This is generally a central position. A pair of clearance arrows are shown in FIG. 7. Clearance 60 depicts the clearance provided by the contoured 48 in cooperation with the lower edge 58 of vane 40. Meanwhile the clearance P is shown which depicts the larger clearance between the lower edge 58 and the prior art circular shroud reference previously described as line 70. From this embodiment, one skilled in the art can clearly see the reduced differential that the contour 48 provides.

Referring now to FIG. 8, a second extreme position of the vane 40 is depicted, for example at the 25 degree position. Again the clearance 60 is much smaller than the prior art clearance P as related to the circular shroud reference 70.

It should be understood by one skilled in the art that vanes may take various shapes and forms depending upon the design characteristics of the engine. Accordingly, the shape of the contours may be formed to correspond to the shape of the vane lower edge through a preselected arcuate motion. The shroud surface, spindle angle, amount of vane chord overhang and travel are all designed/optimized with reduced clearance for reduced loss and improved performance in mind when optimizing the variable vane system.

Referring now to FIG. 9, a chart is shown depicting a relationship between the vane's angle measured in degrees and the clearance between the vane lower edge 58 and the shroud chord overhang 46. As shown by the line 80, having diamond-shaped data points, the clearance between an angle of minus 10 degrees and 25 increases rather constantly. The stator shroud 32 of this prior art embodiment is circular in shape and is lacking the contour shape of the instant embodiments. To the contrary, line 82 represented by square-shaped data points begins at the previously defined range of minus 3 degrees and moves to a position of 25 degrees. The clearance represented by line 82 is generally constant from about 0 degrees to about 12 degrees, before increasing up to the 25 degree position. Thus, by comparing the data points along the lines 80, 82 one skilled in the art will recognize the clearance is much less in the contoured stator shroud than that of the prior art.

The foregoing description of structures and methods has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. Features described herein may be combined in any combination. Steps of a method described herein may be performed in any sequence that is physically possible. It is understood that while certain forms of a contoured stator shroud have been illustrated and described, it is not limited thereto and instead will only be limited by the claims, appended hereto. 

What is claimed is:
 1. A contoured stator shroud vane assembly in a gas turbine engine having an inlet end, an outlet end and a plurality of propulsor components, comprising: a stator shroud having a generally circular cross-section; said shroud having a forward end, an aft end and at least one surface extending between said first end and said second end; said shroud having a plurality of pivots disposed circumferentially about said shroud to support a trunnion of a vane; said at least one surface of varying elevation adjacent to said plurality of pivots, and extending in a circumferential direction.
 2. The contoured stator shroud vane assembly of claim 1, said surface of varying elevation of at least one surface disposed adjacent an edge of said vane.
 3. The contoured stator shroud vane assembly of claim 2, said surface of varying elevation being curved to approximate the curvature defined by rotation of said edge of said vane.
 4. The contoured stator shroud vane assembly of claim 3, wherein said vane overhang and said surface of varying elevation inhibit leakage when said vane pivots.
 5. The contoured stator shroud vane assembly of claim 1, said plurality of pivots each receiving buttons of a plurality of vanes.
 6. The contoured stator shroud vane assembly of claim 1, said axes of curvature of said surface of varying elevation being generally parallel to an engine axis.
 7. A contoured stator shroud, comprising: a forward end, an aft end and at least one surface extending between said forward end and said aft end; said at least one surface being tapered from said forward end to said aft end; a plurality of areas of varying elevation disposed about said at least one surface, said plurality of areas each having a peak and a valley; a plurality of pivot apertures spaced about a forward end of said at least one surface.
 8. The contoured stator shroud of claim 7, said plurality of areas of varying elevation being curved from a first elevation to a second elevation in a circumferential direction.
 9. The contoured stator shroud of claim 7, said plurality of varying elevation being linear from a first elevation to a second elevation in a circumferential direction.
 10. The contoured stator shroud of claim 7, said shroud changing elevation in an axial direction.
 11. The contoured stator shroud of claim 10, said changing elevation being curved.
 12. The contoured stator shroud of claim 10, said changing elevation being linear.
 13. The contoured stator shroud of claim 7 further comprising a vane having a lowermost edge.
 14. The contoured stator shroud of claim 13, said lowermost edge engaging said plurality of areas of varying elevation during pivoting movement of said vane.
 15. The contoured stator shroud vane assembly of claim 7, said plurality of areas of varying elevation additionally being curved to approximate the curvature defined by rotation of a lower edge of a vane.
 16. A contoured stator shroud, comprising: a forward end and an aft end, at least one surface extending between said forward end and said second end; said at least one surface having a scalloped chord overhang area, said scalloped area extending in a circumferential direction; a plurality of vane mounting locations disposed circumferentially between said forward end and said aft end.
 17. The contoured stator shroud of claim 16, said scalloped chord overhang area being curved from a lower elevation of said stator shroud to an upper elevation of said stator shroud.
 18. The contoured stator shroud of claim 16 further comprising a plurality of vanes operably connected to said plurality of vane mounting locations.
 19. The contoured stator shroud of claim 18, said plurality of vanes each having an edge extending between a leading edge and a trailing edge.
 20. The contoured stator shroud of claim 19, said edge engaging a scalloped chord overhang area during pivoting movement of said vane. 